1. Field of Inventions
The present inventions relate generally to devices for performing diagnostic and therapeutic operations on body tissue.
2. Description of the Related Art
There are many instances where diagnostic and therapeutic elements (referred to herein collectively as “operative elements”) must be positioned adjacent to body tissue. One instance involves the formation of therapeutic lesions to the treat cardiac conditions such as atrial fibrillation, atrial flutter and arrhythmia. Therapeutic lesions may also be used to treat conditions in other regions of the body including, but not limited to, the prostate, liver, brain, gall bladder, uterus and other solid organs. Typically, the lesions are formed by ablating tissue with one or more electrodes. Electromagnetic radio frequency (“RF”) energy applied by the electrode heats, and eventually kills (i.e. “ablates”), the tissue to form a lesion. During the ablation of soft tissue (i.e. tissue other than blood, bone and connective tissue), tissue coagulation occurs and it is the coagulation that kills the tissue. Thus, references to the ablation of soft tissue are necessarily references to soft tissue coagulation. “Tissue coagulation” is the process of cross-linking proteins in tissue to cause the tissue to jell. In soft tissue, it is the fluid within the tissue cell membranes that jells to kill the cells, thereby killing the tissue. Depending on the procedure, a variety of different electrophysiology devices may be used to position a plurality of electrodes at the target location.
In recent years, devices such as surgical soft tissue coagulation probes that carry one or more diagnostic or therapeutic elements have been developed. These probes may be used, for example, in endocardial and epicardial procedures where access to the heart is obtained by way of a thoracostomy, thoracotomy or median sternotomy. Such probes also allow endocardial lesions to be formed as a secondary procedure during a primary open heart surgical procedure such as mitral valve replacement, aortic valve replacement, and coronary artery bypass grafting. In either case, it is frequently desirable to create continuous linear lesions for therapeutic purposes.
Tissue contact can be an issue in any electrophysiology procedure, including those which involve the use of surgical probes for diagnostic and therapeutic purposes. The failure to achieve and maintain intimate contact between the tissue and operative elements can result in gaps in what were intended to be continuous linear lesions. Such gaps may result in a failure to cure the patient's arrhythmia and atrial flutter or may create atrial flutter. Moreover, atrial flutter created by gaps in linear lesions can difficult to cure. Poor contact between the tissue and operative elements can also result in lesions that are not transmural. Lesion which are not transmural may, in turn, fail to cure the patient's arrhythmia or other medical condition.
Another issue in electrophysiology procedures is operative element positioning and, more specifically, preventing the operative elements from moving after the physician has placed them adjacent to the target tissue region.
Tissue temperature can also be an issue in lesion creation procedures. For example, a relatively wide deep lesion may be created by reducing the temperature of the tissue closest to the electrode(s). This shifts the hottest iso-thermal region deeper into the tissue, thereby enabling higher power to be delivered without causing char or excessive surface desiccation to occur. Higher power, in turn, results in a larger volume of tissue being heated to a temperature sufficient to coagulate tissue (above 50° C.) and, therefore, a wider and deeper lesion.